xdiff: rename "struct group" to "struct xdlgroup"

Commit e8adf23 (xdl_change_compact(): introduce the concept
of a change group, 2016-08-22) added a "struct group" type
to xdiff/xdiffi.c. But the POSIX system header "grp.h"
already defines "struct group" (it is part of the getgrnam
interface). This happens to work because the new type is
local to xdiffi.c, and the xdiff code includes a relatively
small set of system headers. But it will break compilation
if xdiff ever switches to using git-compat-util.h.  It can
also probably cause confusion with tools that look at the
whole code base, like coccinelle or ctags.

Let's resolve by giving the xdiff variant a scoped name,
which is closer to other xdiff types anyway (e.g.,
xdlfile_t, though note that xdiff is fond if typedefs when
Git usually is not).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

xdiff/xdiffi.c

@@ -708,7 +708,7 @@ static int score_cmp(struct split_score *s1, struct split_score *s2)
  * Note that loops that are testing for changed lines in xdf->rchg do not need
  * index bounding since the array is prepared with a zero at position -1 and N.
  */
-struct group {
+struct xdlgroup {
 	/*
 	 * The index of the first changed line in the group, or the index of
 	 * the unchanged line above which the (empty) group is located.
@@ -725,7 +725,7 @@ struct group {
 /*
  * Initialize g to point at the first group in xdf.
  */
-static void group_init(xdfile_t *xdf, struct group *g)
+static void group_init(xdfile_t *xdf, struct xdlgroup *g)
 {
 	g->start = g->end = 0;
 	while (xdf->rchg[g->end])
@@ -736,7 +736,7 @@ static void group_init(xdfile_t *xdf, struct group *g)
  * Move g to describe the next (possibly empty) group in xdf and return 0. If g
  * is already at the end of the file, do nothing and return -1.
  */
-static inline int group_next(xdfile_t *xdf, struct group *g)
+static inline int group_next(xdfile_t *xdf, struct xdlgroup *g)
 {
 	if (g->end == xdf->nrec)
 		return -1;
@@ -752,7 +752,7 @@ static inline int group_next(xdfile_t *xdf, struct group *g)
  * Move g to describe the previous (possibly empty) group in xdf and return 0.
  * If g is already at the beginning of the file, do nothing and return -1.
  */
-static inline int group_previous(xdfile_t *xdf, struct group *g)
+static inline int group_previous(xdfile_t *xdf, struct xdlgroup *g)
 {
 	if (g->start == 0)
 		return -1;
@@ -769,7 +769,7 @@ static inline int group_previous(xdfile_t *xdf, struct group *g)
  * following group, expand this group to include it. Return 0 on success or -1
  * if g cannot be slid down.
  */
-static int group_slide_down(xdfile_t *xdf, struct group *g, long flags)
+static int group_slide_down(xdfile_t *xdf, struct xdlgroup *g, long flags)
 {
 	if (g->end < xdf->nrec &&
 	    recs_match(xdf->recs[g->start], xdf->recs[g->end], flags)) {
@@ -790,7 +790,7 @@ static int group_slide_down(xdfile_t *xdf, struct group *g, long flags)
  * into a previous group, expand this group to include it. Return 0 on success
  * or -1 if g cannot be slid up.
  */
-static int group_slide_up(xdfile_t *xdf, struct group *g, long flags)
+static int group_slide_up(xdfile_t *xdf, struct xdlgroup *g, long flags)
 {
 	if (g->start > 0 &&
 	    recs_match(xdf->recs[g->start - 1], xdf->recs[g->end - 1], flags)) {
@@ -818,7 +818,7 @@ static void xdl_bug(const char *msg)
  * size.
  */
 int xdl_change_compact(xdfile_t *xdf, xdfile_t *xdfo, long flags) {
-	struct group g, go;
+	struct xdlgroup g, go;
 	long earliest_end, end_matching_other;
 	long groupsize;
 	unsigned int blank_lines;